This invention relates to reflected wave object detection systems, and more particularly to elimination of narrowband interference appearing in wideband returns.
In a wideband object detection system, narrowband interference may enter a system's detector and inhibit detection of desired wideband signals. An example of a wideband object detection system is pulse compression radar. In a pulse compression radar system a conventional narrow pulse, wideband radar signal is generated and expanded by some means such as a delay line circuit prior to transmission. A wideband signal is thus transmitted. The wideband return is received and coupled through a complementary circuit which compresses the return signal for processing by the radar system. In this manner, a radar system may utilize the power capability of a long pulse system while maintaining the resolution available with a narrow pulse system. An example of pulse compression radar is found in U.S. Pat. No. 3,216,013 -- Thor issued Nov. 2, 1965 and assigned to General Electric Company, the assignee herein. In such a system, reception of a narrowband signal at the same frequency as the compressed pulse which is processed by the system may inhibit detection of the wideband signal which is compressed.
Prior systems have been provided which provide noise limiting of an entire wideband signal. While such systems are effective, they decrease dynamic range. For example, if a non-linear device is used which limits 10db on wideband noise in a system having an 18db compression ratio, the maximum a target will compress will be 8db above noise. For systems incorporating video blanking in high clutter (ground return) environments, it is advantageous to maintain full dynamic range in order to avoid blanking target returns in clutter.